Heretofore, a bulk molding compound (hereinafter abbreviated to BMC), which is a thermosetting resin, has been used as a material for a light reflector such as a reflector and extension used for an automotive lamp and others. Whereas the BMC is excellent in the heat stability and dimensional stability, it has problems that the molding cycle time is long, elimination of burrs requires much time and effort at the time of molding, and productivity is low. As a means for solving the problems, investigations as to a possibility of using a thermoplastic resin have been conducted.
In examples in which a thermoplastic resin is used, thermoplastic resin compositions prepared by blending various reinforcing materials with a crystalline resin typified by a polyester resin such as a polybutylene terephthalate and polyethylene terephthalate, or with a non-crystalline resin typified by a polycarbonate resin have specifically been used.
For instance, a method is proposed in which a composition prepared by using a polyethylene terephthalate resin as thermoplastic resin and blending inorganic fillers such as glass fibers and talc particles therewith as reinforcing material is used (see Laid-open Japanese patent publication No. Hei 6-203613).
In this method, however, it is necessary to smoothing the surface of a molded article by subjecting it to an undercoat treatment in advance of the formation of a light reflecting metal layer on the surface of the molded article, since the surface smoothness of the molded article is insufficient due to the inorganic fillers raised on the surface of the molded article or poor mold release characteristic (hereinafter, the term “mold release characteristics” is simply referred to as release characteristics). When the undercoat treatment is not performed, a mirror surface is not developed even if a light reflecting metal layer was formed, and thus a satisfiable light reflector can not be obtained. Besides, the performance of the undercoat treatment has such problems that an extra step becomes necessary, a treatment of a solvent for dissolving an undercoating material is required, an extra amount of energy is required since a step for drying a coated paint becomes necessary, and further a load imposed against the environment is large.
As a method in which such undercoat treatment is not required, a direct vapor deposition (direct deposition) method is proposed in recent years. In the direct deposition method, a light reflecting metal layer is directly formed on the surface of a molded article, without subjecting the surface of the molded article to an undercoat treatment, by directly vapor depositing a metal on the surface of a molded article or vapor depositing a metal on the surface of a molded article after the molded article was subjected to a plasma activating treatment. In this direct deposition method, an extent of smoothness of the surface of a molded article higher than that heretofore achieved has come to be sought, since a metal layer is directly formed on the surface of a molded article.
Further, there is a trend lately that a high-power lamp is used to increase the luminance. When a high-power lamp is used, the temperature in a head lamp is increased. Accordingly, a material to be used as a substrate of a reflector has come to be required to have a heat resistance of 160 to 180° C. However, as to a light reflector produced by the direct deposition method, a problem that a light reflecting metal layer tarnishes when the light reflector was used for a long time in an environment at such high temperature (that is, a problem of thermal tarnishing) is particularly remarkable. There are several type of phenomena of the thermal tarnishing. Specifically, (1) a phenomenon in which a metal layer is peeled off a substrate resin by a thermal deformation (reduction of the surface smoothness) of the substrate resin (orange peel like defect), (2) a phenomenon in which a substrate resin and a metal layer are peeled from each other or deformed by a gas generated by the thermal decomposition of the substrate resin (whitening), and (3) a phenomenon in which a substrate resin and a metal layer are peeled from each other or deformed by an exudation or bleeding of a component such as an additive contained in the substrate resin (whitening) can be mentioned.
In order to solve this problem, various attempts have been carried out. For example, a resin composition prepared by blending, as a reinforcing material, 3 parts by mass of talc particles which have an average particle diameter of 3 μm and surfaces of which is not treated, with 100 parts by mass of a thermoplastic resin composition comprising a polyalkylene terephthalate resin and a polycarbonate resin (see Laid-open Japanese patent publication No. Hei 11-241006) and a resin composition prepared by blending 12 to 25 parts by mass of talc particles treated with an epoxysilane and having an average particle diameter of 2.6 to 3.8 μm with 100 parts by mass of a polyester resin (see Laid-open Japanese patent publication NO. 2003-12903) are proposed. In addition, various other attempts have been carried out to solve the problem of the thermal tarnishing. For example, a resin composition prepared by blending an inorganic filler, antioxidant, and internal lubricant with a polybutylene terephthalate resin (see Laid-open Japanese patent publication 2000-35509) and a resin composition prepared by blending an inorganic reinforcing material and wax with a resin composition comprising a polybutylene terephthalate resin and polyalkylene naphthalate resin (see Laid-open Japanese patent publication No. 2002-179895) are proposed.
However, the resin composition disclosed in Japanese patent publication No. Hei 11-241006 has problems that the affinity between the resins and the inorganic filler is poor since the inorganic filler used as reinforcing material is not subjected to a surface treatment, the inorganic filler particles are easy to agglomerate together since they have such a very fine particle diameter as 0.3 μm, and the surface smoothness of a molded article to be obtained is not sufficient.
Resin composition disclosed in Laid-open Japanese patent publication No. 2003-12903 has a problem that the surface smoothness of a molded article is not sufficient since inorganic filler particles having a relatively large average particle diameter in the range of 2.6 to 3.8 μm are used as reinforcing material. Besides, since an epoxysilane is used in the resin composition as surface treating agent for the inorganic filler particles, the resin composition has another problem that unreacted epoxysilane is exuded or bled to the surface of a molded article at the time of molding to react the surface of a mold thereby deteriorate the release characteristics. As the result, a defect (release mark) is developed on the surface of a molded article due to the deteriorated release characteristics, and the release mark is transferred as it is on a light reflecting layer to produce a further defect when a light reflecting metal layer was directly formed on the surface of the molded article.
Resin compositions disclosed in Laid-open Japanese patent publication No. Hei 11-241006 or Laid-open Japanese patent publication No. 2003-12903 have a problem that the reflective appearance of a light reflector is dull when a light reflector is produced by directly forming a light reflecting metal layer on the surface of a molded article prepared by employing one of the resin compositions, since talc particles are used as reinforcing material.
Resin composition disclosed in Laid-open Japanese patent publication No. 2000-35509 is intended to repress the thermal tarnishing (whitening) by repressing the generation of a gas due to the thermal decomposition of a substrate polyester resin (phenomenon described in (2) above) by making the amount of terminal carboxyl groups less than a specified amount. However, whereas the resin composition disclosed in the patent publication 2000-35509 mentioned above has no problem when a small-sized and simple-shaped molded article such as a flat plate of 50 mm square is produced from the composition, a problem of a molding defect (defect in the surface smoothness of a molded article, development of a release mark, and others) is caused due to poor release characteristics when such a large-sized molded article having a complex and three dimensional shape as a reflector and extension is produced, since a releasing agent is not contained as a component in the resin composition.
Resin composition disclosed in Laid-open Japanese patent publication No. 2002-179895 is intended to increase the heat resistance of a substrate by employing a polyalkylene naphthalate resin and to repress the thermal tarnishing (orange peel like defect) by repressing the reduction of the surface smoothness of a substrate when heated (phenomenon described in (1) above). However, the resin composition disclosed in the patent publication 2002-179895 mentioned above causes problems of thermal tarnishing (whitening) and release mark since calcium montanate (Hostalub CaV102) or pentaerythritol tetraester of montanic acid (Hostalub WE40) is used in the resin composition as wax releasing agent. Whereas a resin composition containing calcium montanate is good in release characteristics, the resin composition causes the thermal tarnishing (whitening) since the calcium montanate exudes or bleeds when a molded article was placed in an environment at a high temperature. When the pentaerythritol tetraester of montanic acid is used, whereas the thermal tarnishing (whitening) is small, release mark or other defects due to poor release characteristics are developed since the tetraester is small in its effect to the release.
As will be understood from the above, a thermoplastic resin composition which satisfies both of the problem of the thermal tarnishing and the problem of release characteristics at the same time has not existed heretofore.
On the other hand, an automotive head lamp in which a reflector and extension are used has a problem that a volatile component is generated from a resin which is exposed to a high temperature at the time of lighting a light source, and the volatile component adheres to a lens portion to cloud the lens surface since the head lamp has a structure in which a device for the light source, reflector, extension, and others are installed in a vessel sealed with a case (housing) in which a lens and parts are housed. Clouding of the lens surface is called fogging, and it is also an important technical subject for a reflector made of a resin and for a material employed for preparing an extension to solve the problem of the fogging. Investigations for repressing the fogging by incorporating an epoxy containing substance in a thermoplastic polyester resin were carried out (see Laid-open Japanese patent publication No. 2001-316573). However, even in the resin composition disclosed in the patent publication 2001-316573, the problem of tarnishing (thermal tarnishing) of a light reflecting metal layer described above still remains.
Further, even if the problems described above were solved in the aspect of the performance of a material, a new fact has become clear that a condition (surface roughness of a mold), which did not present a problem when a light reflecting metal layer is formed after a conventional undercoat treatment was carried out on the surface of a mold, produces another problem depending on the type of a material. It is a problem that the surface roughness (projections and depressions) of a mold is transferred on the surface of a molded article depending on the type of a molding material; and thus if a mold which has the same extent of a surface condition (surface roughness) as that of a conventional mold which was heretofore used when an undercoat treatment is carried out in advance for producing a light reflector was used, the clarity of image becomes poor. More specifically, since the projections and depressions transferred from a mold to a molded article are extremely small, if an undercoat treatment was performed, the projections and depressions are smoothed, and thus no problem was presented heretofore. However, when a light reflecting metal layer was directly formed on the surface of a molded article for a light reflector without applying an undercoat to the surface of a mold in advance, the projections and depressions transferred to the surface of a molded article affect the reflecting characteristics of a light reflector. As the result, only a light reflector having a poor image clarity was obtained heretofore.